USB Loader GX - starting game gives black screen

I have a quite new Wii, Korean model, premodded with NeoGamma R8 beta 15

there is also Homebrew installed on it.

I have prepared a SD card with files from Wii_Softmod_030310 package and usb_loader_GX_270210
I start the USB Loader, everything works fine, I can start a game from DVD, import a game to USB disk, get covers and so on but when I tryes to start a game on the USB disk everything goes black and it stays there.